The present invention relates to a device for dispensing of a powdered drug preparation by inhalation. The device is in particular a multiple-dose device without propellant gas, equipped with a means for preparing a dose to be inhaled and a means for preventing overdosing. The device of the invention is useful, for example, in the treatment of asthma.
The administering of a powdered drug preparation by inhalation from an inhaler is known. Multidose type powder inhalers comprising a drug container and a metering member for measuring and dispensing a unit dose are also known, for example from patent publications GB 2165159, EP 79478, and EP 166294. In these devices, a series of dosing recesses are notched into the surface of a cylindrical metering member. When the metering member is rotated, e.g. by pressing an actuation member, the dosing recesses will move first to a position in alignment with the powder container for being filled and thereafter to a position in alignment with the inhalation channel, whereupon an unit dose will fall by gravity from the dosing recess into the inhalation channel. Thereafter the dose of medicament is inhaled from the inhalation channel. These devices have the drawback that they make overdosing of the medicament possible by allowing the user to actuate the device repeatedly, whereby plurality of doses are dispensed into the inhalation channel. The user may then inadvertently draw a multiple dose by one inhalation.
Attempts have been made to solve the above-mentioned problem by using dispensing systems in which the dosing recess will not be emptied into the inhalation channel by gravity but, instead, the dose of medicament is inhaled directly from the dosing recess, such recesses having been notched into the surface of a metering member having the shape of a cylinder, a cone or a truncated cone, as disclosed in patent publications WO 92/00771 and WO 92/09322. However, the possibility of overdosing is not entirely eliminated, since repeated actuation of the device by the user is still possible. Overdosing is possible e.g. if the device is shaken between repeated actuations.
Recently, arrangements have been described to prevent unintentional multiple metering operations.
Thus, in the powder inhaler described in U.S. Pat No. 5,263,475, when an actuator (a push-button) is depressed, a spring biased slider slides into a groove and locks the push-button in depressed position. The lock can be released by pushing the slider manually back to its initial position.
More complex designs have also been described where the inhalation force is used to release the lock of the metering member. Since repeated actuation of the device without inhalation is not possible, it is ensured that only one dose at a time is dispensed from the inhalation channel to the lungs of the patient.
Thus, the powder inhaler shown in U.S. Pat. No. 5,447,151 comprises a locking rod. When the device is actuated by depressing a pusher, air is compressed in a chamber and the compressed air pushes the locking rod against the horizontal wall of the pusher. When the pusher is released, a valve arrangement maintains the air pressure in the chamber such that when the pusher is in its rest position, the compressed air pushes the locking rod into a corresponding hole in the horizontal wall of the pusher. The pusher is then locked in its rest position and can not be operated. Inhalation through the inhalation channel causes the chamber to come into balance with atmospheric pressure, whereby the locking rod returns from the locking position to its rest position.
WO 97/00703 describes a powder inhaler comprising an actuating button connected to a metering lever that moves a metering member between filling and dispensing positions and a valve flap. When the actuating button is depressed, the metering lever moves the metering member to the dispensing position. A lug of the metering lever engages with a recess of the valve flap shaft, thereby locking the metering member to the dispensing position. The sucking in of air for inhalation is sufficient to rotate the valve flap and release the metering lever again.
WO 94/11044, WO 97/20589 and WO 99/38555 describe powder inhalers where the movement of the metering member from the filling position to the inhalation position is completed by the inhalation force of the user. Thus, a powdered dose enters the inhalation channel only when sufficient inhalation intensity is produced.
The powder inhaler described in WO 94/28957 is actuated by first pulling and then pushing a metering slide. If the actuating procedure is not followed by subsequent inhalation, a fresh metering operation is prevented by a hook like connection between an air throttle disposed in the inhalation channel and a spring incorporated into the top of the dosing slide. Upon inhalation the air throttle in the inhalation channel is opened and the hook connection undone for next metering operation.
Finally, in a powder inhaler described in WO 93/03782 the dose is inhaled while keeping the metering element button depressed. A sphere positioned in a channel which is inclined in the gravitational force direction, is used as a blocking member. The metering element has a finger that extends through a hole into the area of the blocking sphere. In its rest position the sphere blocks the metering operation. If the air stream is strong enough, the sphere moves in the channel thus allowing the metering operation by permitting the entry of the finger in the channel. This design requires the user to coordinate the actuation and inhalation steps when using the device.
The above arrangements for preventing unintentional multiple metering operations are structurally complex or require a close coordination between the metering operation and the inhalation by the patient. Therefore, there is a need for an improved powder inhaler eliminating the risk of unintentional overdosing.